The 3-dimentional morphology of polypropylene/Ethylen-propylenen-diene monomer (PP/EPDM) blend was analyzed by electron microscope using a new sample preparation method and it was found that the morphology of this blend is much more complex than what has been reported so far. It is found that depending on the scale of observation, the morphology is co-continuous or matrix-disperse. Independent of the employed procedure for blending, in a wide range of compositions, the space is filled with micro particles which have co-continuous internal structure. When the viscosity ratio of the two phases is near unity; the EPDM phase in this co-continuous structure, is formed from nanoparticles which are connected together. The size of micro particles do not change significantly by variation of the viscosity of EPDM phase, but decrease by increasing the viscosity of PP. Furthermore, this scale-dependent morphology has considerable thermal stability. A new mechanism based on surface solubility of PP and EPDM was revealed in order to explain these results. It seems that some chains which get involved simultaneously in both phases act as surfactants. The chains of that phase which has more solubility in the other (PP chains), are the more effective surfactants. According to the Bancraft’s rule in emulsions, this surfactant cause the PP phase to remain the continuous phase even at high EPDM contents. Furthermore, during the formation of EPDM nanodroplets by sheeting mechanism, this surfactant chain which has solved in two droplets, keeps the two droplets connected together like a bridge, and prevents them from separation consequently, a large 3-dimentional structure is formed by nanodroplets sewn together. When hydrodynamic forces break this structure, microdroplets are developed. The size of these microdroplets will be determined mainly by balance between the Stokesian hydrodynamic forces and the bridging forces. At high EPDM contents where phase inversion takes place, this scale-dependent morphology is not observed; instead, multiple droplets consisting of small EPDM droplets in large PP drops are developed which are placed in the continuous EPDM phase. The formation of these multiple droplets is also explained by Bancraft’s law. Since the PP chains act as the more effective surfactant; in the fine PP drops a big entropic repulsion between surfactant chains will be produced; therefore, small EPDM droplets inter to the PP droplets in order to increase PP particles and decrease this entropic repulsion. After dynamic vulcanization, microparticles develop clusters. The size of these clusters is directly proportional to the rate of vulcanization to shear rate. Key Words Morphology, Polymer blend, Thermoplastic olefin, Thermoplastic vulcanizate, PP, EPDM